1. Field of the Invention
The present invention relates to a measuring head, and particularly to a seesaw type measuring head which is used in a machine control gauge, a surface roughness, and contour shape measuring apparatus, or the like.
2. Description of the Related Art
A linear voltage differential transducer (LVDT) is conventionally used for a sensor for measuring displacement of a contact element in a seesaw type measuring head used in a machine control gauge, a surface roughness and contour shape measuring apparatus, or the like.
FIG. 22 is a schematic diagram of this conventional measuring head. A measuring head 110 shown in FIG. 22 is a measuring head for measuring an outer diameter, in which two seesaw mechanisms are combined. In the conventional measuring head 110, a moving amount of a contact element 114 supported rotatably around a support point member 111 is measured as a change in voltage in an LVDT 115 provided in a side opposite from the support point member 111. The measurement value of the LVDT 115 is processed in a control unit 140, and obtained as the moving amount.
However, since the conventional measuring head 110 uses the LVDT for the sensor, the following problems exist. Namely, since the linear range of the LVDT is narrow the measuring range is narrow (generally, about 1 mm) and measurement in a wide range cannot be performed.
Moreover, two of a large master and a small master for calibration are necessary for calibration of indicated dimensions. For example, when a work having a diameter of 30±0.01 mm is measured, a master having a diameter of 30.01 mm (large master) and a master having a diameter of 29.99 mm (small master) are used to adjust sensitivity of the measuring head.
Especially in the case of the measuring head having a size shift function of making it possible to respond to a several kinds of work diameters with one measuring head, the large and small masters are necessary for each dimension to be measured. For example, in the case of the measuring head corresponding to the diameter difference of 20 mm, the zero point can be set at anywhere within the range of 20 mm, but the measurement range is about 1 mm, and therefore when three kinds of works are to be measured, the total of six large and small masters are needed. This is because the linearity of the LVDT differs according to the locations.
Further, setting for measurement takes time due to change of arrangement and a calibration operation by the masters and the like. Since the measuring head is unfavorable in the temperature property and adjustment and inspection for correction thereof take much time, and it takes time until the measuring head is stabilized after the power is turned on, it is unfavorable in actuation property. These are the problems.
In order to solve these problems, a digital measuring head adopting an optical digital mechanism, which moves linearly, is proposed in Japanese Utility Model Application No. 62-078462. However, with the content disclosed therein, a mechanism for converting a moving amount of a contact element supported rotatably around a support point member into a moving amount of linear movement needs to be provided.
However, there exists the problem that the mechanism for converting the rotational movement into the linear movement has a complicated structure, which leads to raise the cost and deteriorates the response frequency due to increase in the mass of a moving portion and friction of the link support point, and therefore it is not applicable to the surface roughness measuring head which is required for high-speed response frequency property.